According to the developments of optical measurement techniques in recent years, there have become possible the observation with an optical microscope and the capturing of a microscopic image (the determination of the position of a two-dimensional or three-dimensional image) through the detection and measurement of faint light at a single fluorescent molecule level. For instance, as described in patent document 1, etc., in accordance with a microscope device consisting of a laser scan type confocal microscope and a super sensitive photodetector, a condition in a sample is imaged by detecting light from a micro region which is a region where the light is detected in the microscope (Hereinafter, referred to as a “light detection region”) while moving the light detection region in the sample so as to scan the inside of the sample. In the case of the optical system of such a confocal microscope, since the light emitted from the outside of the light detection region is blocked and not allowed to reach the photodetector, the detection and measurement of the faint light at a single fluorescent molecule level or a single photon level are possible, and therefore, the imaging with such faint light becomes possible. Further, as an alternative way of the optical microscopic observation and the capturing of a microscopic image with faint light at a single fluorescent molecule level, as described in patent document 2, etc., there have been proposed microscope devices using evanescent light, also. In the cases of such microscope devices using evanescent light, excitation light is given only to a thin region of about 100 nm near the surface of a cover glass and there occurs no light emission from regions other than the thin region, and thus, background light in a microscopic image is greatly reduced, and thereby, an image with faint light at a single fluorescent molecule level or a single photon level will be obtained.
By the way, in patent documents 3-8, etc., Applicant of the present application proposed a new optical analysis technique which enables detecting a light-emitting particle distributed or dissolved in liquid (hereinafter, referred to as “scanning molecule counting method”). In this scanning molecule counting method, the optical system, such as those of a confocal microscope and a multiphoton microscope, which can detect light from a micro area in solution, is used, in which the position of the light detection region is moved, namely, the inside of the sample solution is scanned with the light detection region, and when the light detection region encompasses a light-emitting particle distributed and moving at random in the sample solution, the light emitted from the light-emitting particle is detected individually, and thereby, one by one, light-emitting particles in the sample solution are detected so that the counting of the light-emitting particles and the acquisition of the information on the concentration or the number density of the light-emitting particles in the sample solution becomes possible.